The focus of the investigation into Spain's worst rail accident for 40 years remains on the train's driver, Francisco Garzón, who has been under arrest in hospital since Thursday evening.

Garzón has so far refused to answer police questions, the Press Association reported. He was now expected to questioned by a judge, it said.

At least 78 people died in the accident in which the high-speed Alvia 151 train careered into a sharp curve at more than twice the permitted speed before hurtling off the tracks. By Friday night, 31 were critically ill in hospital, some of them in comas.

Antonio del Amo, head of the Spanish national police's central forensic unit, said six of the bodies recovered from the wreckage had yet to be identified.

On Friday, more reports of Garzón's actions leading up to the crash began to emerge. The daily El País reported that the experienced 52-year-old driver had received an order to reduce speed just seconds before the crash and had acknowledged it by pressing a button in the driver's cab. It remained unclear whether he had been unable or unwilling to apply the brakes on the train, which was running five minutes behind schedule.

A stream of leaked extracts from recorded conversations immediately following the disaster suggested that Garzón held himself responsible for what had happened.

While still trapped in the cockpit of his train, he was reported to have told the emergency service of the state-owned train operator, Renfe: "I hope there are no dead, because they will be on my conscience." He added: "I should have been going at 80 [kph] and I am going at 190." Garzon also reportedly said over and again: "We're human, we're human."

The Spanish news agency Europa Press reported that during the same conversation the driver had said: "I've fucked it. I want to die."

Contacted by telephone in hospital by the regional newspaper, La Voz de Galicia, Garzón refused to comment beyond saying, "You imagine how I am."

Details also began to emerge of Garzón's life. He is a lifelong railwayman and native of Galicia, living in the city of A Coruña with his widowed mother, who lost her other son in a car accident. But he was born in Monforte, an important regional rail centre, and has a flat there.

The son of a railway worker, Garzón was brought up in housing built for railway workers and went to a school run by Renfe. It was in Monforte, 70 miles inland from Santiago de Compostela, that he began working for the company in his early 20s.

He had 10 years' experience as a driver and Renfe's president, Julio Gómez-Pomar Rodríguez, said Garzón had worked on the Ourense to Santiago line, where the accident took place, for more than a year.

Before returning to his native Galicia, he had worked on the line between Madrid and Barcelona, which is served by so-called AVE trains that can reach speeds of 310kph (193mph).

Julia Morais, a friend of his own age in his home town of Monforte de Lemos, told Reuters: "He was sensible and very good at his job. We don't know what could have happened."

Garzón's professionalism appeared to have been compromised by the discovery of a photograph he posted to his Facebook page showing his speedometer at 200kph. However, as a driver of high-speed trains he may have been on a stretch of the network where such a speed is permitted. The photograph was posted on 8 March 2012. It nevertheless surprised Garzon's friends. One wrote: "You're going like the bloody clappers, lad. Brake."

Garzón is suspected of criminal recklessness, but has not yet been charged. Spanish rail experts have argued that mere negligence cannot explain the crash: that the "black boxes" recovered from the train will show that a technical fault was partly – or perhaps entirely – to blame for what happened. Garzón reportedly tested negative for alcohol following the crash.

Garzón was led from the scene of the tragedy with his face covered in blood and given nine stitches to a head wound, but appeared otherwise uninjured.

Meanwhile, in the pilgrimage city of Santiago de Compostela, a shrine to the victims of the rail disaster was forming spontaneously at the entrance to the great cathedral of St James.

Thursday was the feast of St James and the day many of the pilgrims to the traditional site of his tomb in the cathedral aim to complete their journeys. Some tied little bunches of flowers to the railings at the entrance. Others placed candles and notes on the ledges below. Nearby, a stack of pilgrims' staffs leant against the wall.

A day for the ending of journeys was appropriate for remembering those who on Wednesday failed to complete theirs. In many cases it was sheer chance that some of the passengers aboard the Alvia 151 lived and others died.

Carmen Quiroga from A Coruña had switched to a later train because she stood a better chance of dining aboard in peace. As soon as her son heard of the accident, he rang her mobile, but it was out of range. "When I eventually spoke to him, he began to weep: he thought I was there," she told La Voz de Galicia.

Benito Estévez changed his plans after learning from his parents that a relative had been taken to hospital, seriously ill. "I feared that I'd never see him again," he said.

Others were as unlucky as Quiroga and Estevez were fortunate. A young man at the scene of the accident who declined to be named said he had swapped seats on the way up from Madrid with a woman who was killed when the train derailed.

Father Ricardo Vázquez, the spiritual director of the seminary in Santiago, was among those on hand to provide comfort at the centre where relatives of the victims learned of their loved ones' fate. Among the "devastated human beings" he attended was a man who "was crying out that he wanted to die because he felt responsible for the death of his daughter whom he had persuaded to come and visit him".

Manuel Suárez, a sales representative from near Santiago, often travelled to Madrid for his work, but never by rail. "He always went by car or plane," said a cousin. "But on this occasion, he said: 'This time, I'll go by train.'"

• This article was amended on 29 July 2013. An earlier version referred to the feast of St James as having occurred on Friday (26 July), rather than Thursday (25 July).